Thestrongtrendsinclimatechangealreadyevident,thelikelihoodof further changes occurring, and the increasing scale of potentialclimateimpactsgiveurgencytoaddressingagriculturaladaptationmore coherently. There are many potential adaptation optionsavailable for marginal change of existing agricultural systems,often variations of existing climate risk management. We showthat implementation of these options is likely to have substantialbeneﬁts under moderate climate change for some cropping sys-tems. However, there are limits to their effectiveness under moresevere climate changes. Hence, more systemic changes in resourceallocation need to be considered, such as targeted diversiﬁcationof production systems and livelihoods. We argue that achievingincreased adaptation action will necessitate integration of climatechange-related issues with other risk factors, such as climatevariability and market risk, and with other policy domains, such assustainable development. Dealing with the many barriers to ef-fective adaptation will require a comprehensive and dynamicpolicyapproachcoveringarangeofscalesandissues,forexample,fromtheunderstandingbyfarmersofchangeinriskproﬁlestotheestablishment of efﬁcient markets that facilitate response strate-gies. Science, too, has to adapt. Multidisciplinary problems requiremultidisciplinary solutions, i.e., a focus on integrated rather thandisciplinary science and a strengthening of the interface withdecision makers. A crucial component of this approach is theimplementation of adaptation assessment frameworks that arerelevant, robust, and easily operated by all stakeholders, practi-tioners, policymakers, and scientists.

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griculture is the major land use across the globe. Currently

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1.2–1.5 billion hectares are under crops, with another 3.5billion hectares being grazed. Another 4 billion hectares of forestare used by humans to differing degrees, whereas, away from land,globalfisheries areused veryintensively, often beyond capacity(1).Tomeetprojectedgrowthinhumanpopulationandpercapitafooddemand, historical increases in agricultural production will have tocontinue, eventually doubling current production (e.g., ref. 2). Agriculture is also a major economic, social, and cultural activity,and it provides a wide range of ecosystem services. Importantly,agriculture in its many different forms and locations remains highlysensitive to climate variations, the dominant source of the overallinterannual variability of production in many regions and a con-tinuingsourceofdisruptiontoecosystemservices.Forexample,theEl Nin˜o Southern Oscillation phenomenon, with its associatedcycles of droughts and flooding events, explains between 15% and35% of global yield variation in wheat, oilseeds, and coarse grains(3). This existing sensitivity explains why a changing climate willhave subsequent impacts on agriculture. Hence, it has becomecritical to identify and evaluate options for adapting to climatechange in coming decades. Here we use the term ‘‘adaptation’’ toinclude the actions of adjusting practices, processes, and capital inresponse to the actuality or threat of climate change, as well asresponsesinthedecisionenvironment,suchaschangesinsocialandinstitutional structures or altered technical options that can affectthe potential or capacity for these actions to be realized (4).We argue there is a strong rationale for an increasing focus onadaptation of agriculture to climate change. This need arises fromseveral considerations:1. Past emissions of greenhouse gases have already committedthe globe to further warming of

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0.1°C per decade forseveral decades (5), making some level of impact, andnecessary adaptation responses, already unavoidable.2. The emissions of the major greenhouse gases are continuingto increase (6), with the resultant changes in atmosphericCO

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concentration, global temperature, and sea level ob-served today already at the high end of those implied by thescenarios considered by the Intergovernmental Panel onClimate Change (IPCC) (7). Furthermore, some climatechange impacts are happening faster than previously con-sidered likely (5). If these trends continue, then moreproactive and rapid adaptation will be needed.3. There is currently a lack of progress in developing globalemission-reduction agreements beyond the Kyoto Protocol,leading to concerns about the level of future emissions andhence climate changes and associated impacts.4. The high end of the scenario range for climate change hasincreased over time (5, 8, 9), and these potentially higherglobal temperatures may have nonlinear and increasinglynegative impacts on existing agricultural activities (1).5. Climate changes may also provide opportunities for agricul-tural investment, rewarding early action taken to capitalizeon these options (10).Thereisanimmensediversityofagriculturalpracticesbecauseof the range of climate and other environmental variables; cultural,institutional, and economic factors; and their interactions. Thismeans there is a correspondingly large array of possible adaptationoptions.Theobjectivesofthispaperarefirsttooutlinetheseoptionsfor cropping and livestock systems, forestry, and fisheries, using theliterature on crop yields as an example to assess the benefits of adaptation; and second, to suggest some general pathways that canhelpmovefromtechnicalassessmentofadaptationoptionstomorepractical action. Accordingly, we identify some preconditions formoreeffectiveuptakeofadaptations;developanadaptationframe- work to engage all decision makers (farmers, agribusiness, andpolicymakers) that builds on the existing substantial knowledge of

agricultural systems; and outline how science itself needs to adaptto remain relevant in this issue.

Results

Adaptation: What Is in It for Us?

The purpose of undertakingagricultural adaptation is to effectively manage potential climaterisks over the coming decades as climate changes. Adaptationresearch undertaken now can help inform decisions by farmers,agrobusiness, and policy makers with implications over a range of timeframes from short-term tactical to long-term strategic (1).However, it is particularly important to align the scales (spatial,temporal, and sectoral) and reliability of the information with thescale and nature of the decision. For example, short-term climateadaptation by farmers may be accomplished by taking into accountlocal climate trends if there is a strong correspondence betweenthese trends and projected climate changes, or it may be via climateforecasting at scales from daily to interannual. However, farmersmayfindlimitedutilityinlong-termprojectionsofclimate,giventhehigh uncertainties at the finer spatial and temporal scales at whichtheir decisions are made (11). In contrast, the general trends atlargertimeandspatialscalesabletobemorereliablyprojectedwithcurrentclimatemodelsmaybequiteusefulforinputintopolicyandinvestment analyses, provided potentially critical factors are incor-porated such as changes in climate extremes (12). A significantbenefit from adaptation research may be to understand howshort-term response strategies may link to long-term options toensure that, at a minimum, management and/or policy decisionsimplemented over the next one to three decades do not underminethe ability to cope with potentially larger impacts later in thecentury. In the sections below, we try to identify other key benefitsfrom an increased focus on climate change adaptation.

Keeping Policy Relevant.

At the current relatively early stage of thedebate, it is understandable that climate change adaptation islargely being dealt with in isolation from other issues (although seeref. 13). However, over time, this situation needs to evolve so thatclimate change is linked with a much broader set of policies. Inparticular, there is a need for linkage with existing policies onclimate risk such as those on drought or structural adjustment, which otherwise may become poorly targeted. Climate change willrequire these policies to become more dynamic, to cope with thehigh level of uncertainty in the timing and magnitude of potentialclimate changes and the rapidly evolving knowledge base. Further-more, climate change adaptation policies will interact with, dependon, or perhaps even be just a subset of policies on sustainabledevelopment and natural resource management, such as thosenecessary to regulate genetically modified organisms, protect hu-man and animal health, and foster governance and political rights,among many others. This process is often referred to as the‘‘mainstreaming’’ of climate change adaptation into policies in-tendedtoenhancebroadresiliencetoriskortopromotesustainabledevelopment (4, 14). The critical issues of how climate change andadaptation may affect food security and trade and the risk of malnourishment are dealt with in a companion paper (13).

Informing Mitigation Targets.

Importantly, identifying and evaluat-ing possible adaptation strategies are of fundamental value todetermine a set of dynamic climate policy options that lead to the‘‘avoidance of dangerous anthropogenic interference’’ component(Article 2) of the United Nations Framework Convention onClimate Change (65). This is because maximizing societal welfareunder future climate risk will likely involve a mix of both mitigationand adaptation; the percentage contribution of each strategy willdepend on monetary and nonmonetary cost/benefit analyses. Forexample, we would expect the size and cost of the adaptation taskto be lower if there is effective, but perhaps costly, mitigation andhigher if there is no mitigation. Similarly, the benefits of adaptation will be a function of the nature of climate change and the scale of impact. Consequently, inadequate consideration of adaptation op-tions could result in the vulnerability to climate change beingsignificantly overstated, giving rise to more severe mitigation tar-gets. Additionally, mitigation policies can affect the range of adaptation options that practitioners have at their disposal (e.g.,subsidizing biofuel production strongly influences the market foragricultural produce). Another perspective is that implementingeffective adaptation can ‘‘buy time’’ until an effective mitigationresponse can be mounted. Hence adaptation analyses may be usedto inform both the magnitude and timing of mitigation. Achieve-ment of this complex task of effectively integrating mitigationimpacts and adaptation to inform public policy development re-mainsasignificantchallengeforthescientificcommunity,althoughsomestudiesarenowemerging(15).Thisinteractionofscienceandpolicy needs to evolve as the scientific knowledge base changes andmay also focus attention on the importance of integrative ratherthan disciplinary science within the science–policy interface (16).

Informing Investment.

Adaptation analyses can also help informgovernments and industry of the investment or disinvestmentdecisions they need to make now or in the near future in relationto climate-sensitive aspects of their portfolios (e.g., ref. 1). Inparticular, this applies to long-term investments such as plant andanimal breeding programs; building capacity in the scientific anduser communities; developing quarantine systems; establishingperennial crops and forest plantations; purchasing or selling land;or building (or decommissioning) major infrastructure such asdams and water distribution systems, flood mitigation works, andstorage and transport facilities. Climate risks are, of course, onlyone consideration within more complex decision-making processes(10). For example, in Western Australia, increased risk of droughtunderglobalwarmingwasintegratedwithprojectionsofpopulationgrowth, economic development, and social norms in relation to water use, resulting in the construction of a major new dam anddevelopment of other new water sources (17).

Rewarding Early Adopters.

Participatory research into climatechange adaptation options can help agricultural decision makersrealize that acting on the existing trends in climate now is likely tobe to their advantage (e.g., ref. 18). For example, in northeast Australia, crop management that has continuously adjusted to theprogressivereductioninfrostrisk experiencedoverthepastseveraldecades can almost double gross margins when compared withmanagement based on either the long-term risk or managementthat does not consider frost risk (19). Participatory engagement withdecisionmakers,bybringingtheirpracticalknowledgeintotheassessment, can also identify a more comprehensive range of adaptationsthanaretypicallyexploredbyscientists,aswellasbeingable to assess the practicality of options and contribute to morerealistic assessment of the costs and benefits involved in manage-ment or policy change (19).

Focusing on Climate Risk Management.

Finally, it should be recog-nized that ‘‘adaptation’’ is an ongoing process that is part of goodrisk management, whereby drivers of risk are identified, and theirlikely impacts on systems under alternative management are as-sessed. In this respect, adaptation to climate change is similar toadaptation to climate variability, changes in market forces (cost/price ratios, consumer demands, etc.), or institutional or otherfactors. Differences may be in the rate of realized climate change,comparedwithhowfastweareabletoimplementneededsolutions.Isolating climate change from other drivers of risk may be helpful,especially during the initial stages of assessment when awareness of the relative importance of this risk factor is still low. Operationally,however, translating adaptation options into adaptation actionsrequires consideration of a more comprehensive risk managementframework. This would allow exploration of quantified scenariosdealing with all of the key sources of risk, providing more effective

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decision making and learning for farmers, policymakers, andresearchers: an increase in ‘‘climate knowledge’’ (20).

Changing Management Unit Decisions

Changes in practices at the management unit level will be a keycomponent in adapting agriculture to climate change (1). Conse-quently, we outline here a range of such adaptations for cropping,livestock,forestry,andfisherysystems.However,adaptationsatthislevel can be strongly influenced by policy decisions to establish orstrengthen conditions favorable for effective adaptation activitiesthrough investment in new technologies and infrastructure (4), which are dealt with below.

Cropping Systems.

Many management-level adaptation options arelargely extensions or intensifications of existing climate risk man-agement or production enhancement activities in response to apotential change in the climate risk profile (1). For croppingsystems,therearemanypotentialwaystoaltermanagementtodeal with projected climatic and atmospheric changes (including refs.21–26). These adaptations include:

Y

Altering inputs such as varieties/species to those with moreappropriate thermal time and vernalization requirementsand/or with increased resistance to heat shock and drought,altering fertilizer rates to maintain grain or fruit qualityconsistent with the prevailing climate, altering amounts andtiming of irrigation and other water management.

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Wider use of technologies to ‘‘harvest’’ water, conserve soilmoisture (e.g., crop residue retention), and use and transport water more effectively where rainfall decreases.

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Managing water to prevent water logging, erosion, and nutri-ent leaching where rainfall increases.

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Altering the timing or location of cropping activities.

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Diversifying income through altering integration with otherfarming activities such as livestock raising.

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Improving the effectiveness of pest, disease, and weed man-agement practices through wider use of integrated pest andpathogen management, development, and use of varieties andspecies resistant to pests and diseases and maintaining orimproving quarantine capabilities and monitoring programs.

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Using climate forecasting to reduce production risk.If widely adopted, these adaptations singly or in combinationhavesubstantialpotentialtooffsetnegativeclimatechangeimpactsand to take advantage of positive ones. For example, in a modelingstudy for Modena, Italy (23), simple and feasible adaptationsaltered significant negative impacts on sorghum (

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48% to

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12%). In that case, theadaptations were to alter varieties and planting times to avoiddroughtandheatstressduringthehotteranddriersummermonthspredicted under climate change. When summarized across manyadaptation studies, there is a tendency for most of the benefits of adaptingtheexistingsystemstobegainedundermoderatewarming(

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2°C) then to level off with increasing temperature changes(Table 1; ref. 27). Additionally, the yield benefits tend to be greaterunder scenarios of increased than decreased rainfall (Table 1),reflecting that there are many ways of more effectively using moreabundant resources, whereas there are fewer and less-effectiveoptionsforsignificantlyamelioratingriskswhenconditionsbecomemore limiting.The figures in Table 1 are from a synthesis of climate changeimpact simulations for the recent Intergovernmental Panel onClimateChangereview (1), spanningthemajor cerealcrops wheat,rice,andmaize,andrepresentingawiderangeofagroclimaticzonesand management options. This synthesis indicates that benefits of adaptation vary with crop (wheat vs. rice vs. maize) and withtemperature and rainfall changes (Table 1; ref. 1). For wheat, thepotential benefits of management adaptations are similar in tem-perateandtropicalsystems(17.9%vs.18.6%;Table1).Thebenefitsfor rice and maize are smaller than for wheat, with a 10% yieldbenefit when compared with yields when no adaptation is used (1).These improvements to yield translate to damage avoidance of upto1–2°Cintemperateregionsandupto1.5–3°Cintropicalregions,potentially delaying negative impacts by up to several decades (1),providing valuable time for mitigation efforts to work.There are several significant caveats that need to be applied inrelation to the above positive results on impacts and adaptation. Inparticular, the simulation models used in the component studies donotyetadequatelyrepresentpotentialimpactsofchangeinpestanddisease effects or air pollution, and there remains uncertainty as tothe effectiveness of the representations of CO

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responses (2). Additionally, many of these studies changed neither the variabilityof the climate nor the frequency of climate extremes, both of whichcan significantly affect yield (2). There is also often the assumptionof full capacity to implement the adaptations, whereas this may notbe the case, particularly in regions where subsistence agriculture ispredominantly practiced (28). Last, some of the studies were of irrigated production systems where the implications of possiblereductions in irrigation water availability are not included (29).Collectively, these factors could reduce the beneficial effects, suchas those associated with elevated CO

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, and increase the negativeeffects, such as those from increased temperatures and rainfallreductions. This would reduce the amount of time that adaptation would delay significant negative impacts, i.e., adaptation would‘‘buy less time’’ than is indicated above. On the other hand, theadaptations assessed were only a small subset of those feasible,usually focusing on marginal change in practices to maintain theexisting system such as changing varieties, planting times, and useofconservationtillage.Inclusionofabroaderrangeofadaptations,including more significant and systemic change in resource alloca-tions, would presumably increase the benefits, particularly if thoseadaptations included alternative land use and livelihood options.For instance, so-called Ricardian studies (30) that implicitly incor-porate such adaptation routinely find impacts of climate changethat are lower than those assessed using crop models. The balancebetween these opposing tendencies is currently unclear; morecomprehensive analyses to identify the limits of adaptation are warranted.